In conventional projection type display devices, there is a device that obtains dustproof effect by covering the entire device with a protection case (for example, see Patent Document 1). In addition, as devices that target particular components mounted on the device, not the entire device, there is a device that reduces the attachment of dust particles to a light tunnel or color wheel, (Patent Document 2), and there is a device that cleans a rod integrator soiled due to the attachment of dust particles (Patent Document 3).
In the following, these examples of conventional dustproof techniques will be described.
The technique disclosed in Patent Document 1 is one in which the entire device is enclosed and dust-proofed using a protection cabinet mounted with an air filter and air intake fans. The outside air is admitted by the air intake fans through the air filter, dust particles contained in the air are removed, and then the air is delivered to the entire device. Because all the air admitted passes through the air filter, the entire device can be dust-proofed.
The technique disclosed in Patent Document 2 is one in which unnecessary light, when light enters the light tunnel or color wheel is shielded with a light shielding plate, and thermal storage due to the light received on the light shielding plate is moved to the outside of a mirror chamber for heat dissipation. Because temperature rises in the light tunnel, the color wheel, and the air in the inside of the mirror chamber can be suppressed, the internal airflow is reduced, and consequently, airborne dust particles are prevented from becoming attached to optical components.
The technique disclosed in Patent Document 3 is in which that a cleaning pad is operated by a mechanical means for physically cleaning the light emitting face of the rod integrator.
[Patent Document 1] JP-A-2003-241310 (page 6, FIG. 1, page 7, and FIG. 5)
[Patent Document 2] JP-A-2002-318423A (page 1 and FIG. 2)
[Patent Document 3] JP-A-2005-292680A (page 6 and FIGS. 1 and 2)
However, in the technique disclosed in Patent Document 1, the air filter is used, and an air filter having a fine mesh is necessary in order to remove dust particles in a small particle size. However, because the air filter having a fine mesh collects dust particles in a middle or large particle size, too, the air filter tends to be clogged and has a high ventilation resistance. What is required is to increase the filter area in order to reduce ventilation resistance, so that a large-sized air filter is necessary. Moreover, this technique requires that the air intake quantity be in creased in order to dust-proof the device and also requires that plurality of large-sized or middle-sized fans be used that can secure large quantity of air.
Furthermore, if the device is installed in adverse dust particle environments, the air filter is sometimes clogged even though a large-sized air filter is used. When the air filter is clogged, it is not possible to deliver sufficient tempering air to components in the inside of the device, causing temperature rises in the components, so that the lifetime of the components shortens. Many optical components are particularly sensitive to temperature, and they deteriorate considerably due to temperature rises, causing color irregularities or a reduction in brightness in projection images.
In other words, the protection cabinet enclosing the entire device is large and heavy, and the protection cabinet is also required to have high sealing properties in order to prevent air intake other than through the air filter. In addition, in adverse dust particle environments, it is also likely to clog the air filter.
On the other hand, the structure disclosed in Patent Document 2 does not operate in the case where there are no dust particles near the light tunnel or color wheel, and if dust particles are present, the structure can reduce the attachment of dust particles to the optical components, but the structure cannot completely prevent particles from becoming attached to the optical components. In addition, because the light other than the unnecessary light is incident on optical components such as the light tunnel or color wheel, it is not possible to reduce temperature rises in the components caused by this light. In reality, because the temperature rises in these optical components are greatly caused by necessary light except unnecessary light for the light projection, a large temperature rise occurs when the internal airflow is reduced, sometimes leading to the deterioration or destruction of the optical components.
Moreover, the technique disclosed in Document 3 is one in which the cleaning pad is contacted with the light emitting face of the rod integrator for cleaning, so that the light emitting face is sometimes damaged when the cleaning pad wipes dust particles. This particularly tends to occur in the case where dust particles are sand dust, and in the case where the light emitting face is damaged, there is a problem in that brightness is considerably reduced because light is diffused. Furthermore, it is necessary to provide a space for mounting the mechanical means that operates the cleaning pad, causing a high probability of malfunction because of the provision of a plurality of operating units.